BEIJING (AP) — Travelers in China were blocked from buying plane tickets 17.5 million times last year as a penalty for failing to pay fines or other offenses.

The Chinese government reported this week on penalties imposed under a controversial “social credit” system the ruling Communist Party says will improve public behavior.

The system is part of efforts by President Xi Jinping’s government to use data-processing and other technology to tighten control over society.

Human rights activists say “social credit” is too rigid and might unfairly label people as untrustworthy without telling them they have lost status or how to restore it.

The National Public Credit Information Center says people and companies were blacklisted for offenses ranging from failure to pay taxes to false advertising or violating drug safety rules.